Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
IronPort-SDR: oBIbuDpW/CUFvPlcNDPK257QBt6t1Mpd1sHcuklF4sTmwEy9hX/Vh1P60d7JLY/J7rbi/fzNZq
 A6w5wLBjy9XAi9rFoiklxyHFLjkNf9XovGA6GmWRpXFzfVP/UtmGMzxyEC2DLQ7iORnKTr4+6v
 7Ag+xM7m1GQZHHvuUWhLLebXNi4LbeJrQqum4rfrBwzW3OVY2n4lUaaYaqpAdNF3hlYZLucLCd
 w0DrBRfc7l8XV3Tm+Ux/TGLcExIzvp0oFUPCJGMkuE6B8UWHlJBmgAtK3hXfYIUrr+S5Y2dJZc
 lpU=
From:   Avri Altman <Avri.Altman@wdc.com>
To:     Stanley Chu <stanley.chu@mediatek.com>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        "martin.petersen@oracle.com" <martin.petersen@oracle.com>,
        "alim.akhtar@samsung.com" <alim.akhtar@samsung.com>,
        "jejb@linux.ibm.com" <jejb@linux.ibm.com>,
        "asutoshd@codeaurora.org" <asutoshd@codeaurora.org>
CC:     "beanhuo@micron.com" <beanhuo@micron.com>,
        "cang@codeaurora.org" <cang@codeaurora.org>,
        "matthias.bgg@gmail.com" <matthias.bgg@gmail.com>,
        "bvanassche@acm.org" <bvanassche@acm.org>,
        "linux-mediatek@lists.infradead.org" 
        <linux-mediatek@lists.infradead.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kuohong.wang@mediatek.com" <kuohong.wang@mediatek.com>,
        "peter.wang@mediatek.com" <peter.wang@mediatek.com>,
        "chun-hung.wu@mediatek.com" <chun-hung.wu@mediatek.com>,
        "andy.teng@mediatek.com" <andy.teng@mediatek.com>,
        "chaotian.jing@mediatek.com" <chaotian.jing@mediatek.com>,
        "cc.chou@mediatek.com" <cc.chou@mediatek.com>
Subject: RE: [PATCH v4] scsi: ufs: Fix imprecise load calculation in devfreq
 window
Thread-Topic: [PATCH v4] scsi: ufs: Fix imprecise load calculation in devfreq
 window
Thread-Index: AQHWP7Al3AIqrrCrYk65auU9x8ZVS6jTDYNg
Date:   Thu, 11 Jun 2020 08:03:35 +0000
Message-ID: <SN6PR04MB46405CE4B375BA3134D64A99FC800@SN6PR04MB4640.namprd04.prod.outlook.com>
References: <20200611052109.22700-1-stanley.chu@mediatek.com>
In-Reply-To: <20200611052109.22700-1-stanley.chu@mediatek.com>
Accept-Language: en-US
Content-Language: en-US
wdcipoutbound: EOP-TRUE
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: a6047aa5-633d-4494-48d9-08d80dddf103
X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Jun 2020 08:03:35.4603
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: IUE6UhcLjP+AbV20WkuXLglIM+yBjLWwPzMqOln4Pp7tT4sru9B8C9NspmroWIQfggCF0vCzGj3qKpRHlGSA6Q==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR04MB5311
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


>=20
> The UFS load calculation is based on "total_time" and "busy_time" in a
> devfreq window. However, the source of time is different for both
> parameters: "busy_time" is assigned from "jiffies" thus has different
> accuracy from "total_time" which is assigned from ktime_get().
>=20
> Besides, the time of window boundary is not exactly the same as
> the starting busy time in this window if UFS is actually busy
> in the beginning of the window. A similar accuracy error may also
> happen for the end of busy time in current window.
>=20
> To guarantee the precision of load calculation, we need to
>=20
> 1. Align time accuracy of both devfreq_dev_status.total_time and
>    devfreq_dev_status.busy_time. For example, use "ktime_get()"
>    directly.
>=20
> 2. Align below timelines,
>    - The beginning time of devfreq windows
>    - The beginning of busy time in a new window
>    - The end of busy time in the current window
>=20
> Fixes: a3cd5ec55f6c ("scsi: ufs: add load based scaling of UFS gear")
> Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Reviewed-by: Avri Altman <avri.altman@wdc.com>

Just a small nit.

> -       stat->total_time =3D jiffies_to_usecs((long)jiffies -
> -                               (long)scaling->window_start_t);
> +       stat->total_time =3D ktime_to_us(curr_t) - scaling->window_start_=
t;
ktime_sub ?

Thanks,
Avri